Syntheses, crystal structures and Hirshfeld surface analysis of 2-(benzylsulfanyl)-5-[4-(dimethylamino)phenyl]-1,3,4-oxadiazole and 2-[(2-chloro-6-fluorobenzyl)sulfanyl]-5-[4-(dimethylamino)phenyl]-1,3,4-oxadiazole

The title molecules were synthesized by alkylation of 5-[(4-dimethylamino)phenyl]-1,3,4-oxadiazole-2-thiol. In the crystals, C–H⋯π interactions are observed between neighboring molecules. Hirshfeld surface analysis indicates that H⋯H and H⋯C/C⋯H interactions make the most important contributions to the crystal packing.


Chemical context
For the synthesis of pharmacologically active heterocyclic compounds, a study of the relationship between structure and activity is of great interest. The various five-membered aromatic heterocyclic compounds have a diverse range of action. These include oxadiazoles, consisting of two carbon atoms, two nitrogen atoms and one oxygen atom, which have four different isomeric structures: 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole.

Supramolecular features
In crystal structures of the title compounds, weak intermolecular contacts of the C-XÁ Á Á type are observed. In (I), weak C7A-H7ACÁ Á ÁCg2 interactions link the molecules, forming infinite chains along the b-axis direction (Fig. 3  The asymmetric unit of (II) with atom labeling. Ellipsoids represent 30% probability levels.

Figure 1
The asymmetric unit of (I) with atom labeling. Ellipsoids represent 30% probability levels.

Figure 3
Observed weak intermolecular C7A-H7ACÁ Á ÁCg2 interactions in the crystal structure of (I) (the molecules are linked along the b-axis direction). Table 1 Hydrogen-bond geometry (Å , ) for (I).

D-HÁ
structure (Table 1). In the crystal structure of (II), the formation of an infinite chain is also observed as a result of the C2B-Cl1Á Á ÁCg1 interaction, which links molecules along the c-axis direction (Fig. 4). Intermolecular C8A-H8ABÁ Á ÁCg3 and C7B-H7BAÁ Á ÁCg3 interactions between these chains consolidate the crystal structure (Table 2). In order to visualize and quantify the intermolecular interactions in (I) and (II), a Hirshfeld surface analysis (Spackman & Jayatilaka, 2009)    Observed intermolecular C2B-Cl1Á Á ÁCg1 interactions in the crystal structure of (II) (the molecules are linked along the c-axis direction).

Synthesis and crystallization
A mixture of 5-[4-(dimethylamino)phenyl]-1,3,4-oxadiazole-2thiole (0.005 mol), benzyl chloride or 2-chloro-6-fluorobenzyl chloride (0.005 mol) and K 2 CO 3 (0.005 mol) was boiled in 20 ml of dry acetone for 6 h. The solvent was then removed, the residue washed with water and with 2% NaOH solution to remove unreacted oxadiazolthione, and then washed with water until neutral. The resulting target products were dried in air and recrystallized from ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were positioned geometrically (with C-H distances of 0.97 Å for CH 2 , 0.96 Å for CH 3 and 0.93 Å for C ar ) and included in the refinement in a riding-motion approximation with U iso (H) = 1.2U eq (C) [U iso = 1.5U eq (C) for methyl H atoms]. For (I), the crystal studied was refined as an inversion twin with matrix [1 0 0, 0 1 0, 0 0 1] ; the resulting BASF value is 0.43 (2).